Method and apparatus for metal coating metal pipes by electric fusion



Sept. 16, 1947. o. R. CARPENTER ETAL 2,427,350

METHOD AND APPARATUS FOR METAL COATING METAL PIPES BY ELECTRIC FUSION Filed July 15, 1943 5 Sheets-Sheet 1 fir WW 2 M mPJ m wwd w A O mw Sept. 16, 1947. 0. R. CARPENTER ET AL METHOD AND APPARATUS FOR METAL COATING METAL PIPES BY ELECTRIC FUSION Filed July 15, 1943 5 Sheets-Sheet 2 1% a p w fi mmK M, M? m mad n 1 p 6, 1947. o. R. CARPENTER ETAL 2,427,350

METHOD AND APPARATUS FOR METAL COATING METAL PIPES BY ELECTRIC FUSION Filed July 15, 1945 5 Sheets-Sheet 5 Fig.3

uvvgwm gg Otis B Carpenter Sept. 16, 1947. o. R. CARPENTER ETAL 2,427,350

METHOD AND APPARATUS FOR METAL COATING METAL PIPES BY ELECTRIC FUSION Filed July 15, 1943 5 Sheets-Sheet 4 INVENTORS Oil's P. Carpenter B Haward J Kerr A TTORNE Y Sept. 16, 1947.

o. R. CARPENTEYQEI' AL METHOD AND APPARATUS FOR METAL COATING METAL PIPES BY ELECTRIC FUSION Filed July 15, 1945 5 Sheets-Sheet 5 ATTORNEY Patented Sept. 16, 1947 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR METAL COATING METAL PIPES BY ELECTRIC FUSION Application July 15, 1943, Serial No. 494,796

4 Claims.

This invention relates to metal cladding improvements particularly adapted for the manufacture of retorts to be used in the ferro-silicon (Pidgeon) process of producing magnesium. This process involves the heat treatment of a natural magnesium compound in retorts which are subiected externally to furnacetemperatures of the order of 2100" F. and 2300 F. The retorts are closed and are subjectto a vacuum, chemical reactions takin place under these conditions.

The magnesium is subsequently vaporized and thereafter collected on a. fluid cooled surface within the retort. Because of the oxidizing and corrosive conditions of furnace gases at temperatures in excess of 2100 F., it has been suggested that the retorts be of cast metal, the metal being alloy of high oxidation and corrosion resistance, such as steel containing high percentages of chrome and nickel. However; this suggestion did not result in extensive commercial use because of the fact that such high chrome and high nickel alloys were highly critical materials and were not available in sufficient quantity to produce a large number of retorts required by the capacity of the magnesium industry then predicted. The present invention overcame this difliculty by improvements whereby the retort shell of carbon steel is coated with the critical alloy by a fusion welding process. In the development of the invention, known arc welding methods were tried, but it was found that the retorts produced thereby were of such poor quality and of such short life in the actual magnesium producing process that their use therein was prohibitive. Upon examination of these retorts, the cladding was found to contain a high percentage of impurities believed to be silica and chrome oxide inclusions. The deposited metal was also subject to considerable stress and intergranular cracks to such an extent as to materially shorten the life of the retort. It was also found that the chromium and nickel percentages in the cladding were considerably lower than was considered adequate to present the necessary oxidation resistance.

The present invention overcomes the above indicated difficulties by presenting a method and apparatus for applying the cladding metal in such a way that highly successful retorts of long life are produced. The present invention involves a method of cladding in which electric fusion is employed, and the fusion zone submerged with such a welding mixture that the alloy cladding may be properly bonded to the base metal and the requisite characteristics of the clad metal for (Cl .117-93) I 2 high oxidation resistance and high corrosion resistance may be obtained. The present invention involves a mode of operation in which there is minimum penetration of the base metal due to 5 the relation of the fusible weldrod thereto, and the simultaneous action of the welding mixture to counteract the dilution of the cladding and add oxidation resistant characteristics thereto.

The present invention has been successfully used in the quantity production -of magnesium retorts, having a carbon steel base, clad with a high chromium, high nickel steel alloy coating of a thickness of the order of one half inch, the thickness of the base metal being of the order of one inch. The coating has been of substantially uniform thickness and the metal thereof has been notably free from inclusions which would produce excessive porosity. The surface of the clad coating of the retorts produced by this inzo vention has also been substantially free from cracks, and the desired high percentage of chromium (27%-24%) and nickel (22%-19%) has been maintained. In part, this latter result has been obtained by the controlling of the penetra- 25 tion of the alloy coating into the base metal to minimize the migration of carbon from the carbon steel base into cladding alloy, it being appreciat'ed that any excessive migration of this kind would result in carbide segregation in the grain boundaries of the cladding. The invention also involves the use of a welding compound which not only subme'rges the fusion zone, but has such characteristics that it is self-cleanin from the surface of the clad metal. This has 5 helped materially to maintain high production rates.

The invention will be described with reference to the accompanying drawings which indicate apparatus employed in carrying out the illustrative 40 method.

In the drawings:

Fig. 1 is a perspective view illustrating the welding apparatus in operation;

Fig. 2 is a. rear perspective view of the Fig.

1 apparatus;

Fig. 3 is a. front perspective view of the Fig. 1 apparatus;

Fig. 4 is a plan;

Fig. 5 is a vertical section through the Fig.

1 apparatus taken on the section line 5-5 of Fig. 4 and showing the welding head in elevation;

Fig. 6 is a fragmentary section through a part of the wall of the multiple metal retort taken longitudinally thereof at such a position as that indicated by the line 66 of Fig. 4;

Fig. 7 is a fragmentary view in the nature of a transverse vertical section taken transversely of the retort in the zone of the weldrod; and

Fig. 8 is a fragmentary view showing the relation of the weldrod to a previously deposited head of weld metal. I,

In Fig. 4 of the drawing, the tubular retort member I6 (preferably 01 low carbon steel) is rotatably mounted upon a machine provided with a lead screw I2 which moves the welding head 58 toward one end of the retort member as the alloy coating is deposited. The retort member is fixed in a centering member I6 rotatably supported by the tail-stock structure I6 of the machine. This member is in the nature of a cap provided with three or more centering set screws such as those indicated at 26--22 in Fig. 5.

The opposite end of the retort member I6 is centered and supported in a cap-like structure 24 similar to I6. This structure is provided with centering set screws similar to 26--22. It acts as a head-stock, and is non-rotatively connected to the driving shaft 26.

The retort member I6 is rotated at the desired R. P. M. by power transmitted from the motor 28. The power transmitting connections between the head-stock shaft 28 and the motor include the pulleys 82 and 84, the belt 36. and the speed reducer 38.

The translatory motion of the welding head is co-ordinated with the rate of rotation of the retort member I6 by power transmitting connections between the lead screw and the head-stock shaft 26. These connections include a driving gear 46 non-rotatably fixed with reference to the shaft 26 and meshing with a pinion 42 fixed on the counter-shaft 44. Fixed to this counter-shaft is a gear 46 of larger diameter, meshing with a smaller gear 48. The latter is fixed to a second counter-shaft 48 which transmits power to the lead screw I2 through a clutch or coupling which permits the rotation of I2 without the rotation of the gear drive by a crank handle at th'e opposite end of I2.

The welding head carriage I4, as indicated in Figs. 2 and 5, includes a base plate 56, and rigidly connected structural members such as 52-54, the post 56, side plates, spacers, angles, and roller supports. This carriage supports the welding head 58 and the flux hopper 66, through the laterally extending arm 62 which is vertically and rotatively adjustable with respect to the column 56. The carriage structure is supported by the longitudinal frame members 64 and 86, the former of which acts as a guide to maintain the path of movement of the welding directly parallel to the axis of the retort member I6. 'Io effect this guiding and supporting action, the beam or frame member 64 has an upper guide strip I6 secured thereto in the position indicated in Fig. 5. This guide strip extends longitudinally of the beam 64 and is contacted on its sides by rollers such as I2 and I4, rotatively mounted on the carriage. The top of the strip I6 is contacted by a load carrying roller 16 rotatively mounted on the carriage.

Secured to the bottom flange of the beam 64 is a longitudinal guide strip I8, the surfaces of which are contacted by rollers 86--82 rotatively mounted on the carriage in an arrangement somewhat similar to the arrangement of the previously described rollers. It will be appreciated that, with this arrangement, the welding head will be guided accurately in a path parallel to the longitudinal axis of the retort member.

To further insure accurate movements of the welding head parallel to the retort axis, and to prevent the overhang of the welding head from interfering therewith, the structural frame member 58 of the welding head carriage extends later ally in the same direction as the welding head overhang and rotatively supports a roller 84 riding along the upper surface of the beam 86 as indicated in Fig. 5. The member 53 is directly fixed to the remainder of the carriage structure and is further made rigid therewith by the brace 64.

To translate the rotary motion lead screw I2 into longitudinal movement of the welding head carriage I4, the latter is supplied with an internally'screw threaded member 56. This member is non-rotatively mounted on the carriage and is threaded upon the lead screw.

Th'e welding head support arm 62 extendin from the column 56 may have a split clamping collar 86 formed with substantially parallel radial extensions 82 and 64. This collar may be tightly clamped in the desired angular position upon the column 56 by pressing these extensions toward each other. However, to insure the maintenance of the welding head at a desired elevation, the collar 86 rests upon the subiacent collar 96 which may be adjustably fixed to the post 66 by set screws.

In order that the welding head, and therefore the weldrod I66, may be accurately angulated or otherwise desirably positioned with reference to the welding or cladding zone, the welding head is pivotally supported upon a, rod or trunnion I62 fixed to the outer end of the arm 62. As indicated in Fig. 5, this trunnion has keyed thereto a radial arm I64 pivotally supporting an internally screwthreaded adjustment collar I66 at its lower end. Threaded through this collar is an adjustment screw I68 having a. hand wheel I I6 fixed thereto. The opposite end of the shaft I68 is rotatively mounted in a downward extension II2 of the welding head base II4, the arrangement being such that the operation of the hand wheel III produces relative motion between the extension I I2 and the fixed arm I64. Thus, when the screw I68 is turned by the hand wheel II6, the fusing end of the weldrod I66 and the entire welding head are moved in arcs, the center of which is the center of the trunnion I62. One important purpose and effect of such adjustment on the welding method will be referred to in the following description.

The weldin head includes two motors H6 and I I8, one of which is a constant speed motor. The other is a variabl speed motor with its speed controlled by mechanism not shown, responsive to changes in one or more characteristics of the electric current between the weldrod I66 and the retort member I6 to maintain substantially constant fusion conditions. These motors are connected to appropriate mechanisms to controllably advance the weldrod I66 through the guides I26I 22 to the fusion zone.

In Fig. 7 of the drawings, a partial transverse section of the retort member I6 is indicated, and the direction of rotation of the member I6 is indicated by the arrow I26. The weldrod I66 and the member I 6 are connected to a power source in such a way that electric fusion of the weldrod metal takes place in the gap between the work, or the member I6, and the adjacent end of the weldrod. This fusion takes place normally under a body of granular flux completely submerging'the fusion zone so that no arc can be seen. The fluxflows from the hopper 66 to the fusion zone through a hopper outlet tube I23, and a submerging accumulation of flux is maintained around the fusion zone. This is facilitated by the flux retainer I30 which may be secured to the weldrod guide I2I.

As also indicated in Fig. 7, the fusing end of the weldrod I is positioned at an angle of 18 (plus or minus 1) from a vertical plane through the longitudinal axis of the retort member, the plane being indicated by the line A-B and the direction of the weldrod by the line C-D. The latter is preferably not radially disposed with ref erence to the retort. With a retort member I0, of about 12" diameter, the line E-F indicating the spacing of the fusing end of the weldrod from the vertical A-B is preferably from 1%". to 1 /2" long, the angulation of the weldrod and the spacing of its fusing end from the vertical A-B being controllable by the operation of the adjustin mechanism including the elementsv I06, I08, and I I0, previously described.

For the production of a durable retort for use in the manufacture of magnesium, the retort coating 132 (Fig. 6) must have high oxidation resistance at temperatures of the order of 2100f F.2300 F., and for this purpose the present invention provides a steel alloy coating I32 of high chromium and high nickel content. Austenitic alloy steel weldrods known as 25-20 chromium, 20% nickel) are used and the final oating I32 represented in Fig. 6 consists of two laye s R and S, consisting of the helical overlapping beads. I34 and I36. In so far as the oxidation resistance of the coating is concerned, the chromium content is a critical factor, and considerable difficulty has been experienced in maintaining a sufficiently high percentage in the coating I32. The chief difliculty in this respect has resulted from the dilution of the weld deposited metal by the metal of the base, or retort member I0. Other things being equal, the extent of such dilution depends upon the penetration of the base metal during the welding process, and the angulation of the weldrod (indicated in Fig. 7 of the drawings) has been foundto materially affect such penetration, the arrangement of the weldrod shown reducing the dilution of the coating metal to an optimum degree. Th penetration of the base materially increases as the weldrod I00 is moved toward the position of the line A-B.

In the present method another factor in maintaining the dilution of the coating at a low value is the use of a granular flux containing from 10 to percent of ferro-chrome, the fused metal in the fusion zone at the end of the electrode receiving additional chromium from this source during the welding process. The preferred flux also contains powdered aluminum which during the welding process promotes the absorption of chromium by the weld metal and its distribution therein, by its de-oxidizing action. One and one half to two percent of this material has been found satisfactory for the purposes of the present method. The remainder ofv the preferred flux consists of a mixture of the following materials in the indicated approximate percentages;

Composition A: Per cent Calcium fluoride 23.1 Calcium silicate 20.2 Asbestos 29.9 Aluminum oxide 16.0 Manganese oxide 7.9 Iron oxide 1.6

All of the flux ingredients are ground mixed with sodium silicate and the mixture is then baked-at 400 F., and then finely reground. The entire flux mixture is such that undesirable evolutions of gases do not occur under welding con-' ferro-c'nrome in excess of 15% do no materially increase the chromium absorption, the optimum absorption in the present method being effected at about the 10%-15% range of ferro-chrome constituency.

During the welding process, a substantial part of the. flux is fused, and this fusion, with the fusion of the weld metal causes additional chromium absorption by the deposited metal by reason of the deoxidizing actionof the aluminum powder. The aluminum in the flux also has the further beneficial effect of causing the weld metal to freeze with a very smooth surface. An additional effect of the aluminum is to cause part of the fused flux to solidify in such a manner that when it becomes cooled below 1000 F., it is readily detached from the deposited weld metal which it covers and will automatically drop from the weld metal upon rotation of the tubular member.

The aluminum is distributed throughout the illustrative flux, and it is believed that this distribution, in "combination with the inter-action of the aluminum and ferro-chromium with the other materials of the previously referred to composition A, results in a better absorption and distribution of the chrome from the ferro-chrome into the weld metal.

During the operation of the illustrative method, such beneficial and highly desirable results are produced with respect to the characteristics of the clad surface and with respect to the selfcleanlng action of the flux, that these results are believed to be at least in part due to the presence of residual aluminum in the flux after the oxidation of some of the aluminum has occurred. In

this connection, it is to be noted that the fusion temperature of the aluminum is much less than one half of the mean fusion temperatures of the remaining constituents of the welding compound.

During the development of the invention, tests were made with welding compounds containing no aluminum, and attempts were also made to find successful substitutes for aluminum in the welding compound, but these tests merely served to prove that the illustrative aluminum containing welding compound was notably superior to the other compounds. The illustrative aluminum containing compound, when used in the method of the invention produced the following results in comparison to methods involving welding compounds free from aluminum:

1. The desired high chromium constituency (24%-2'7%) and high nickel constituency (20% were readily attained.

2. The overlapping and contacting helical beads of the-cladding were flatter and smoother, to the end that smooth surface claddings of substantially uniform thickness were produced.

3. The fused and subsequently frozen flux over the surface of the cladding was self-cleaning. When cooled below 1000 F., it automatically removed itself from the clad metal.

4. Gaseous action in the molten pool of fused weld metal was substantially eliminated.

5. Cracks in the surface of the cladding were substantially eliminated. 6. These tests also indicated that a close spacing of the successive helical beads resulted in a mesh screen.

I clearly indicated in the drawings.

marked increase in the chromium content of the cladding. They also showed conclusively that preheating of'the base metal was particularly effective in reducing the cracking in the deposited metal.

Tests proved that the cracking of the weld metal could also be materially reduced and sub- Per cent High carbon ferro-chrome 12.5 Aluminum powders 1% Composition A 86.0

This flux was dry mixed. and then bonded with sodium silicate (approximately 300 grams per hundred pounds of flux) to-form a wet mixture, baked at 400 F., and then mulled to pass a 16 Various tests with different current values of different welding speeds indicated clearly that low current values and low welding speeds were essential requirements of the process. Welding speeds as low as 20 inches per minute and welding currents of 350-380 amperes' and 28-30 volts were found to give superior results. 7

Under optimum conditions, the frozen slag or flux will be automatically freed from the coating metal bead I40 (see Fig. 7), by gravity as the rotation of the retort member I continues. The attainment of smooth surfaced wide weld beads (to form the coating shown in Fig. 6) and the self-cleaning of the previously fused slag (frozen over the weld metal) are attributed (at least in part) to the effect of the aluminum in the flux. It may be that, by reason of the aluminum, the frozen flux has a contraction rate differing suiflciently from that of the weld metal to promote this self-cleaning action, but at any rate, the attainment of the smooth surface of the solidifled flux (previously fused) certainly promotes such self-cleaning.

Immediately beyond the fusion zone at the end of the weldrod I00, and to the right thereof, as the arrangement of work and weldrod is indicated in Figs. and 7 of the drawings, it may be considered that there are three different zones from the base metal radially outwardly. In the inner zone, there is the bead of deposited metal I40 with itshigh chromium, high nickel content. Next outwardly of this zone, there is an intermediate zone in which the flux is fused, or has been fused. As the deposited bead recedes from the weldrod this fused flux progressively freezes or solidifies. In the outer zone there is the excess of granular flux which has not been fused. This excess drops off'the work member as it rotates. The granular flux then passes through a screen 150 which is clearly shown in Figs. 1

and 3. As the work rotates further, pieces of the fused and subsequently frozen flux fall from the work and are caught upon the screen I50 as The excess granular flux falling through the screen I50 into the hopper is returned to the supply in the hopper 27%) of chromium in the weld deposited coating, One of these is the speed of welding, it having been found that a relatively low speed such as twenty inches Der minute will give a chromium value higher than that produced at hig er spe of welding. The second factor is that relatively low current values (350 to 380 amp.) definitely results in increased chromium values. The deposition of the beads in abutting relation with previously deposited beads also increases the chromium content of the coating. I

Another important factor in the production of the illustrative magnesium retort, relates to the relative uniformity of thickness of the coating. To attain this desired result, the coating beads must be relatively wide and without a high crown. These factors also promote the manufacture of a retort of long operative life with the use of a minimum amount of the alloy steel, 'Ihisresult is of considerable importance owing to the fact that such material is highly critical, and relatively scarce under war conditions.

Another characteristic of the present method is that surface cracks in the deposited coating are eliminated. Several factors contribute to this. One is that the carbon content of the deposited metal is held to a very low value. Another factor is the manner of deposition of the weld metal whereby weld metal is deposited against a previously deposited bead before the latter is cooled to a value approaching room temperature. Also, the work, or retort member I 0, is preheated before the coating begins. Another factor of the illustrative method which eliminates the formation of surface cracks is the maintaining of the retort member In within a temperature range of 400 F.-600 F. during the coating operation. To effect this, water at room temperature may be sprayed into the retort member. To maintain some water within the member I 0, its lead end may be closed and the opposite end partially closed by a ring I52 which is fitted against the inner surface of the tubular member. The thickness of this ring is indicated by the dotted circle I52 in Fig. 5. When the temperature of the metal rises, more wateris allowed to pass within the member ID, the quantity of water within the member Ill at all times being limited by the thickness of the ring I52.

Referring to Fig. 8 of the drawings, the overlapping of the beads of deposited metal is promoted by inclining the weldrod at about 5 (plus or minus 1) to the normal to the longitudinal axis of the retort member Ill. As indicated, the weldrod is directed toward a previously deposited bead.

This angular adjustment of the weldrod may be effected or varied by the operation of the hand wheel I58 upon the adjusting shaft I60. The turning of this hand wheel and its shaft moves the weldrod guides Ill and I22 as a unit, about a pivot extending forwardly of the welding head base H4.

For convenience in claiming the invention, clockwise" has been used to designate the normal direction of rotation of the cylinder, or retort member in, and counterclockwise the direction opposite to the normal direction of rotation.

Although the invention has been described with reference to the details of a specific method, and with reference to the details of apparatus for carrying out that method, it i to be appreciated that the invention is not to be considered as limited to all of the details thereof. It is rather to be taken as of a scope commensurate with the scope of the subioined claims.

What is claimed is:

1. In a method of electric fusion weldin upon a cylindrical steel base of relatively high carbon content, the steps comprising effecting rotational movement of the base about a horizontal axi at a peripheral speed of about 20 inches per minute beneath a source of solid coating metal of stainless steel characteristics advancing linearly, fusing the coating material at a position near the termination of a top vertical radius of the base but offset therefrom opposite to the direction of rotation to about 12 of the diameter of the base, cooling the base during the welding process to maintain the temperature thereof except at the weld point between 400 and 600 F., effecting relative movement axially of the base between it and the metal source simultaneously with said rotation to cause the deposition of successive contacting helical beads of weld metal at a rate to form thick beads, continually supplying near and submerging the weld zone and the adjacent bead of weld material under a relatively deep blanket of granular flux containing aluminumto about 1%%, carrying said flux along from the position of initial fusing past the vertical and to the downstream side of the base by said rotation, separating the cooled fused flux by gravity near the bottom of the base, maintaining the welding current at about 400 amperes, and advancing the coating metal along a line tilted backwardly from a radius through the fusion zone.

2. The method as defined in claim 1 in which the line of advance of the source of coating metal is also directed toward the adjacent bead at an angle of substantially 5 to the normal to the base surface at the junction therewith.

3. In apparatus for interfusing an alloy steel coating with the external face of a steel cylinder of small diameter, means effecting clockwise rotation of the cylinder while the latter is held fixed against endwise movement, a consumable alloy weldrod disposed at a position offset counter-clockwise from the vertical including a radius of the cylinder and acting as a source of weld metal for said coating, means constantly submerging the fusing end of the weldrod and the adjacent bead of freshly deposited weld metal in a granular flux containing an appreciable amount of aluminum and an alloy augmenting material, and means effecting movement of the weldrod in 10 a direction axially of the cylinder, said last named means being operative simultaneously with the means for effecting said relative rotation.

4. In apparatus for inter-fusing an alloy steel coating with the external face of a steel cylinder of small diameter, means effecting clockwise rotation of the cylinder while the latter is held fixed against endwise movement, a consumable alloy weldrod disposed at a position offset counter-clockwise from the vertical including a radius of the cylinder and acting as a source of weld metal for said coating, means constantly submerging the fusing end of the weldrod and the adjacent bead of freshly deposited weld metal in a granular flux containing an appreciable amount of aluminum and an alloy augmenting material, means cooling the cylinder to a temperature within the 400 F.-600 F. range to permit a high rate of metal deposition, and means effecting movement of the weldrod in a direction axially of the cylinder, said last named means being operative simultaneously with the means for effecting said relative rotation.

OTIS R. CARPENTER. HOWARD J. KERR.

REFERENCES CITED The following references are of record in the file of this patent:

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